1. Field of the Invention
The present invention relates to new and improved linear motors, especially those linear motors having moving coils. As described herein, the coils of the present invention provide more effective multi-pole, multi-phase structures for use in a linear motor, and the present invention also describes improvements for the dissipation of heat from a linear motor resulting in better performance and/or longevity.
2. Description of the Prior Art
Linear motors which directly produce a linear force in response to an electric current are known, and the prior art has been previously reviewed. For example, U.S. Pat. No. Re. 34,674 notes that linear drives have been used in many areas, including automation and robotic positioning systems, printers and disk drive units. One type of linear motor is, e.g. the linear stepper motor, which is similar to a rotary stepper motor. A second type of linear motor is the moving magnet motor. These motors incorporate a fixed wound stator assembly with the load attached to a moving magnet assembly. Yet another type of linear motor is the moving coil linear motor. These can be either brush or brushless designs having a moving coil passing through an air gap created by either two rows of permanent magnets and magnetic circuit completion means or back iron with one row of permanent magnets and a magnetic circuit completion means using one back iron and one ferromagnetic bar.
However, the moving coil windings in these motors are generally the limiting factor to the force that can be developed due to heat buildup in the windings. The linear force developed is proportional to the current passing through the windings, the number of turns of wire and the flux density in the magnetic circuit. Given a constant flux density and a given number of turns in the windings, force is then proportional to the current in the windings. At the same time, the power to be dissipated as heat is proportional to the resistance of and current in the winding and builds at a rate much greater than the increase in force. This generally results in a current limitation in the coils being required to prevent overheating of the coil assembly.
With regards to the specific linear motor described in U.S. Pat. No. Re. 34,674, said motor was defined as having a central row of alternating permanent magnets, with multi-phase, multi-pole coil assemblies located on both sides of the magnet row. That is, the coil assemblies were said to be formed of a series of individual coils connected in a multi-phase, multi-pole relationship. Two coil assemblies are described, each coil located substantially in a plane parallel to a magnet plane on opposite sides of a magnet row. Furthermore, the coil loop thickness was said to be approximately said individual coil loop total width divided by two times the number of phases, and no foreign material, such as ferromagnetic laminations or other metallic materials, was located in the volume of the coil assembly. Finally, a minimum of two coils per phase were described, in which coils of the same phase are in contact with one another.
Other prior art motor designs and related subject matter has been disclosed, and reference is made to the following U.S. Patents for additional background information: U.S. Pat. No. 4,749,921 "Linear Motor With Non Magnetic Armature"; U.S. Pat. No. 4,331,896 "Zig-Zag Windings, Machine and Method"; U.S. Pat. No. 4,303,017 "Long Stator Linear Motor Without Iron" U.S. Pat. No. 4,369,383 "Linear DC Permanent Magnet Motor"; U.S. Pat. No. 4,575,211 "Brushless D.C. Motor" U.S. Pat No. 3,913,045 "Linear Moving Inductor For Electromagnetic Pumps, Conveyor Troughs or Agitator Reels for Liquid Metals"; U.S. Pat. No. 3,969,644 "Pulse Generator With Asymmetrical Multi-Pole Magnet".
As can therefore be seen from the above, the moving coil windings emerge as a limiting factor to the force that can be developed due to the heat buildup in the windings. That being the case, there has been a long-standing need to develop new and improved coil designs to improve motor performance, i.e., a linear motor which develops large accelerations, static force and speeds, and which does not require large numbers of expensive magnets, and does not have a coil assembly which overheats.
Accordingly, it is a first object of this invention to provide a coil configuration which improves the configurations reported in the prior art, and which can be described in part as containing a coil assembly which contains at least two phases having one coil loop per phase, comprised of individual coil loops of essentially rectangular shape, with end turn areas arranged parallel to the longitudinal axis of a magnetic field wherein an opening is provided within the volume of the coil assembly, and wherein one coil side of the 2nd phase is positioned parallel to and between the coil sides of the first phase for the purpose of improved linear motor performance.
More specifically, and again with reference to the prior art linear motor designs summarized above, such designs have not been optimized for heat removal as the coil assemblies were generally only air-cooled and had poor heat sinking of the coil assemblies. That is, the coils themselves were not fully distributed to provide maximum transfer of heat to a heat sink. Furthermore, the prior art has yet to provide a coil configuration wherein an opening within the volume of the coil loops, as noted above, is specifically located in the end turn areas, disposed along the longitudinal axis of the magnetic path, for the purpose of improving heat dissipation, and for the placement of thermally conductive non-magnetic material for structural support.
Additionally, while linear motors of the prior art contained magnetic circuit completion means, said completion means itself had not been structurally optimized for heat removal, with regards to, as herein described, the use of plates, and plate separating ribs comprising a plurality of air gaps between separating blocks along the magnet track axis.
It is also a primary object of the invention to provide a permanent magnet linear motor which overcomes the disadvantages of the prior art and provides a new and improved coil geometry, including a heat sink attached to opposite end turn areas, that can be described as a heat sink cap to improve motor performance.